Ok I just found this. [Link: parts-express.com]

I think DM blanks the video signal on a DM switcher so that we can do this. I'm not absolutely sure of that.

I would mainly use this with a high performance DAC via USB to an audiophile computer such as this. [Link: computeraudiophile.com]

Some some zones will benefit from this high quality distributions and other zones that only have TV speakers not so much. At least I could easily deliver all sources to all zones in a simple to program solution.